This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2000-015892, filed Jan. 25, 2000 the entire contents of which are incorporated herein by reference.
The present invention relates to a method and apparatus for continuously adsorbing and removing CO2 from waste gas discharged from a boiler of a thermal power plant or from a combustion furnace of an incinerator.
In order to prevent global warming, it is required to regulate release of CO2 (carbon dioxide) gas, which is a greenhouse effect gas, into the atmosphere. One of methods of suppressing the release of the carbon dioxide gas into the atmosphere is to decarbonate waste gas from a thermal power plant or the like by physical adsorption before the waste gas is released into the atmosphere.
An apparatus for physically adsorbing carbon dioxide gas contained in waste gas having four adsorption towers loaded with an adsorbent, which are operated in parallel, is known to the art. In this case, a granular adsorbent or an adsorbent of honeycomb structure is loaded in each adsorption tower. In the apparatus, supply of waste gas at a low pressure and low temperature, carbon dioxide adsorption under pressure, carbon dioxide desorption by heating, and recovery of desorbed carbon dioxide under a reduced pressure are successively repeated in these four adsorption towers so as to carry out the carbon dioxide adsorption and the regeneration of the adsorbent continuously. However, the conventional apparatus is defective in that the apparatus includes four adsorption towers and, thus, requires a large site.
Japanese Patent Disclosure (Kokai) No. 6-91128 discloses another apparatus for physically adsorbing and removing carbon dioxide contained in waste gas. In this apparatus, waste gas of a low temperature and a high pressure and a regenerating gas of a high temperature and a low pressure are allowed to flow counter-currently through a drum rotor loaded with a granular adsorbent. The drum is rotated while allowing these gases to flow through it so as to carry out continuously adsorption of carbon dioxide gas contained in the waste gas and desorption of carbon dioxide gas adsorbed by the adsorbent.
However, in this apparatus, the waste gas itself having a low temperature and a high pressure is used for cooling the adsorbent. Therefore, carbon dioxide gas within the waste gas is unlikely to be adsorbed until the adsorbent heated by the regenerating gas of a high temperature is cooled sufficiently, leading to the defect that the recovery rate of carbon dioxide gas is low. Also, since the flow rate of the waste gas is markedly lowered in the case of using a granular adsorbent, it is necessary to introduce the entire amount of the waste gas from a flue into the apparatus for processing the waste gas. In addition, in order to prevent the granular adsorbent from being moved and distributed unevenly in accordance with rotation of the drum, it is necessary to arrange a plurality of partitioned chambers within the drum, leading to a complex construction of the apparatus.
An object of the present invention is to provide a decarbonating apparatus simple in construction, not requiring a large space, and capable of continuously recovering carbon dioxide gas from waste gas with a high recovery efficiency.
According to the present invention, there is provided a method for decarbonating waste gas, comprising steps of: rotating a drum rotor loaded with a CO2 adsorbent having a honeycomb structure; allowing the waste gas to flow through a region of the drum rotor so as to permit CO2 contained in the waste gas to be adsorbed by the CO2 adsorbent; supplying a heated gas to a region of the drum rotor so as to desorb CO2 from the CO2 adsorbent; and supplying a cooled gas to a region of the drum rotor so as to regenerate the CO2 adsorbent, wherein these steps are performed simultaneously so as to permit the CO2 adsorbent within the rotating drum rotor to be subjected successively to the CO2 adsorption step, the CO2 desorption step and the regeneration step.
According to the present invention, there is provided a decarbonating apparatus, comprising: a drum rotor loaded with a CO2 adsorbent having a honeycomb structure, the CO2 adsorbent being arranged so as to adsorb CO2 contained in waste gas that is allowed to flow through a region thereof; a heated gas supply pipe for supplying a heated gas to a region of the drum rotor so as to permit adsorbed CO2 to be desorbed from the CO2 adsorbent; a cooling gas supply pipe for supplying a cooling gas to a region of the drum rotor so as to regenerate the CO2 adsorbent; a heated gas recovery pipe for recovering the heated gas that has flowed through the CO2 adsorbent; and a cooling gas recovery pipe for recovering the cooling gas that has flowed through the CO2 adsorbent, wherein the drum rotor is configured to rotate with successively passing through the adsorption region for adsorbing CO2 contained in the waste gas, the desorption region to which the heated gas is supplied, and the regeneration region to which the cooling gas is supplied.
In the present invention, it is desirable to provide a purge region, for purging the CO2 desorbed from the CO2 adsorbent, between the desorption region and the regeneration region. It should be noted that the CO2 desorbed from the CO2 adsorbent by the heating gas can be removed to some extent accompanying with the heating gas. However, it is more desirable to employ purging with a purge gas for achieving removal of the desorbed CO2 without fail.
Namely, according to another aspect of the present invention, there is provided a method for decarbonating waste gas, comprising steps of: rotating a drum rotor loaded with a CO2 adsorbent having a honeycomb structure; allowing the waste gas to flow through a region of the drum rotor so as to permit CO2 contained in the waste gas to be adsorbed by the CO2 adsorbent; supplying a heated gas to a region of the drum rotor so as to desorb CO2 from the CO2 adsorbent; supplying a purge gas to a region of the drum rotor so as to purge CO2 desorbed from the CO2 adsorbent; and
supplying a cooling gas to a region of the drum rotor so as to regenerate the CO2 adsorbent, wherein these steps are performed simultaneously so as to permit the CO2 adsorbent within the rotating drum rotor to be subjected successively to the CO2 adsorption step, the CO2 desorption step, the CO2 purging step and the regeneration step.
A decarbonating apparatus for carrying out the method described above comprises: a drum rotor loaded with a CO2 adsorbent having a honeycomb structure, the CO2 adsorbent being arranged so as to adsorb CO2 contained in waste gas that is allowed to flow through a region thereof; a heated gas supply pipe for supplying a heated gas to a region of the drum rotor so as to permit adsorbed CO2 to be desorbed from the CO2 adsorbent; a purge gas supply pipe for supplying a purge gas to a region of the drum rotor so as to purge CO2 desorbed from the CO2 adsorbent; a cooling gas supply pipe for supplying a cooling gas to a region of the drum rotor so as to regenerate the CO2 adsorbent; a heated gas recovery pipe for recovering the heated gas that has flowed through the CO2 adsorbent; a purge gas/CO2 recovery pipe for recovering the purge gas that has flowed through the CO2 adsorbent and CO2 purged from the CO2 adsorbent; and a cooling gas recovery pipe for recovering the cooling gas that has flowed through the CO2 adsorbent, wherein the drum rotor is configured to rotate with successively passing through the adsorption region for adsorbing CO2 contained in the waste gas, the desorption region to which the heated gas is supplied, the purging region to which the purge gas is supplied, and the regeneration region to which the cooling gas is supplied.
In the present invention, it is desirable to provide a dehumidifying section on the high temperature side of the decarbonating section. It should be noted that the CO2 adsorbent adsorbs humidity in preference to CO2. Therefore, if the waste gas contains humidity, the CO2 recovery rate is lowered. Therefore, when CO2 is adsorbed by the CO2 adsorbent after the waste gas is dehumidified, it makes possible to increase the CO2 recovery rate.
Namely, according to still another aspect of the present invention, there is provided a method for decarbonating waste gas, comprising steps of: rotating a dehumidifying drum rotor loaded with a humidity adsorbent having a honeycomb structure and a decarbonating drum rotor loaded with a CO2 adsorbent having a honeycomb structure, the drum rotors being arranged in series; allowing the waste gas to flow through a region of the dehumidifying drum rotor so as to permit humidity to be adsorbed by the humidity adsorbent, followed by allowing the dehumidified waste gas to flow through a region of the decarbonating drum rotor so as to permit CO2 to be adsorbed by the CO2 adsorbent; supplying a heated gas to a region of the dehumidifying drum rotor so as to desorb humidity from the humidity adsorbent, together with supplying a heated gas to a region of the decarbonating drum rotor so as to desorb CO2 from the CO2 adsorbent; supplying a purge gas to a region of the dehumidifying drum rotor so as to purge humidity desorbed from the humidity adsorbent, together with supplying a purge gas to a region of the decarbonating drum rotor so as to purge CO2 desorbed from the CO2 adsorbent; and supplying a cooled gas to a region of the dehumidifying drum rotor so as to regenerate the humidity adsorbent, together with supplying a cooled gas to a region of the decarbonating drum rotor so as to regenerate the CO2 adsorbent, wherein these steps are performed simultaneously so as to permit the humidity adsorbent within the rotating dehumidifying drum rotor to be subjected successively to the humidity adsorption step, the humidity desorption step, the humidity purging step and the regeneration step and so as to permit the CO2 adsorbent within the rotating decarbonating drum rotor to be subjected successively to the CO2 adsorption step, the CO2 desorption step, the CO2 purging step and the regeneration step.
A decarbonating apparatus for carrying out the method described above comprises a dehumidifying section for adsorbing humidity contained in waste gas, and a decarbonating section for adsorbing CO2 contained in the dehumidified waste gas, wherein the dehumidifying section includes: a dehumidifying drum rotor loaded with a humidity adsorbent of a honeycomb structure, the humidity adsorbent being arranged so as to adsorb humidity contained in the waste gas that is allowed to flow through a region thereof; a heated gas supply pipe for supplying a heated gas to a region of the dehumidifying drum rotor so as to permit adsorbed humidity to be desorbed from the humidity adsorbent; a purge gas supply pipe for supplying a purge gas to a region of the dehumidifying drum rotor so as to purge humidity desorbed from the humidity adsorbent; a cooling gas supply pipe for supplying a cooling gas so as to regenerate the humidity adsorbent; a heated gas recovery pipe for recovering the heated gas that has flowed through the humidity adsorbent; a purge gas/humidity recovery pipe for recovering the purge gas that has flowed through the humidity adsorbent and humidity desorbed from the humidity adsorbent; and a cooling gas recovery pipe for recovering the cooling gas that has flowed through the humidity adsorbent; in which the dehumidifying drum rotor is configured to rotate with successively passing through the adsorption region for adsorbing humidity contained in the waste gas, the desorbing region to which a heated gas is supplied, the purging region to which the purge gas is supplied, and the regeneration region to which the cooling gas is supplied, and wherein the decarbonating section includes: a decarbonating drum rotor loaded with a CO2 adsorbent having a honeycomb structure, the CO2 adsorbent being arranged so as to adsorb CO2 contained in the waste gas that is allowed to flow through a region thereof; a heated gas supply pipe for supplying a heated gas to a region of the decarbonating drum rotor so as to permit adsorbed CO2 to be desorbed from the CO2 adsorbent; a purge gas supply pipe for supplying a purge gas to a region of the decarbonating drum rotor so as to purge CO2 desorbed from the CO2 adsorbent; a cooling gas supply pipe for supplying a cooling gas to a region of the decarbonating drum rotor so as to regenerate the CO2 adsorbent; a heated gas recovery pipe for recovering the heated gas that has flowed through the CO2 adsorbent; a purge gas/CO2 recovery pipe for recovering the purge gas that has flowed through the CO2 adsorbent and CO2 purged from the CO2 adsorbent; and a cooling gas recovery pipe for recovering the cooling gas that has flowed through the CO2 adsorbent; in which the decarbonating drum rotor is configured to rotate with successively passing through the adsorption region for adsorbing CO2 contained in the waste gas, the desorption region to which the heated gas is supplied, the purging region to which the purge gas is supplied, and the regeneration region to which the cooling gas is supplied.
In the above decarbonating apparatus, it is desirable to fix the dehumidifying drum rotor and the decarbonating drum rotor to the same shaft so as to be rotated at the same speed in order to increase the CO2 recovery rate. Also, in order to increase cooling effect on the adsorbent performed by the cooling gas, it is desirable that the heated gas and the purge gas are allowed to flow concurrently with the waste gas, and the cooling gas be allowed to flow counter-currently to the waste gas. Further, in order to decrease energy for recovery, it is desirable to arrange heat exchangers for performing heat exchange between each of the heating gases supplied to the dehumidifying drum rotor and the decarbonating drum rotor with the waste gas on a high temperature side.
The decarbonating apparatus of the present invention is arranged in, for example, a flue of waste gas. In this case, each of the dehumidifying drum rotor and the decarbonating drum rotor is mounted such that a part the drum rotor is positioned within the flue, with the other part positioned outside the flue. Also, the heated gas supply pipe, the purge gas supply pipe, the cooling gas supply pipe for each of the drum rotors and the recovery pipes corresponding to these supply pipes are arranged outside the flue.
Also, it is possible for the dehumidifying drum rotor and the decarbonating drum rotor, which are included in the decarbonating apparatus of the present invention, to be connected directly to a low temperature side of an air heater comprising a rotor for performing heat exchange between the waste gas discharged from a combustion furnace and combustion air to be supplied to the combustion furnace.
Further, the present invention provides an air heater having the decarbonating apparatus of the present invention integrally incorporated therein. Namely, the air heater of the present invention comprises an air heater main unit including a rotor performing heat exchange between the waste gas discharged from a combustion furnace and combustion air to be supplied to the combustion furnace, and a dehumidifying section for adsorbing humidity contained in the waste gas and a decarbonating section for adsorbing CO2 contained in the dehumidified waste gas, which are incorporated in the low temperature section of the air heater main unit. The dehumidifying section and the decarbonating section have similar constructions to those described in conjunction with the above decarbonating apparatus.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.